In order to make a sliding or rolling bearing operate satisfactorily it is necessary that the bearing is supplied with a proper volume of lubricant in order always to let a thin lubricant film separate the movable metallic components of the bearing. It is important that this lubricant film has a thickness sufficient to ascertain that metallic contact will not occur, but it shall on the other hand not be too thick, as it then will constitute a resistance against the motions resulting in a temperature increase.
Some bearings are sealed off and lubricated once for all, whereas other bearings require an even supply of lubricant. Those latter bearings are often supplied continuously with lubricant via separate devices.
It has always been the goal of bearing designers to supply the bearing with as small a quantity of lubricant as possible to ensure maintenance of a reliable oil film. Rather small volumes of lubricant have thereby been reached. As an example, it has been found that a lubricant supply of about 3 mm.sup.3 /min for a rolling bearing having an outer diameter of 200 mm is adequate. The desire is, however, to reach still smaller amounts of supplied lubricant, i.e. in the range of 1 mm.sup.3 /min.
However, a new problem arises when supplying such small volumes of lubricant, that is lubricant leakages which are always present, will be considerable in relation to the lubricant volume supplied. This is of particular concern in bearings of the type mounted in two-part housings and wherein lubricant is supplied through channels in the housing and in the outer bearing race ring. Since these channels are partly situated in the interface between the metallic parts, it is virtually impossible to prevent a certain amount of lubricant leakage.